An apparent plot to send two explosive-laden packages by cargo plane from Yemen to the US has focused new attention on Al-Qaeda in the Arabian Peninsula (AQAP).

The network was formed in January 2009 by a merger between two regional offshoots of the international Islamist militant network in neighbouring Yemen and Saudi Arabia. The US president's counterterrorism adviser John Brennan has called it: "the most active operational franchise" of al-Qaeda beyond Pakistan and Afghanistan.

Led by a former aide to Osama Bin Laden, the group has vowed to attack oil facilities, foreigners and security forces as it seeks to topple the Saudi monarchy and Yemeni government, and establish an Islamic caliphate.